In the harvesting of agricultural products, such as, for example, grain, there is a need to detect the respective throughput of harvested crops, whether this be geo-referenced for use in precision agriculture or cumulative for the purpose of exact accounting in paid harvesting work.
Measuring devices have been proposed which detect the volume of the harvested material optically (e.g., DE 198 02 756 A). What is to be considered as a disadvantage here is that the volume can indeed be detected, but not the mass or gravitational force of the material, which is substantially more relevant for said purposes than the volume. A detection of the density of the material and a conversion of the volume into a mass are conceivable, but are complicated and are susceptible to faults on account of the frequently and briefly changing densities of the harvested material.
Furthermore, it has been proposed to detect the mass of the harvested material by weighing the entire grain elevator of a combine harvester (e.g., DE 195 44 057 A). This measurement presents problems in the case of smaller throughputs of harvested crops, since the mass of the harvested crops is then substantially lower than the weighed mass of the grain elevator. A poor signal-to-noise ratio is consequently obtained, which is further impaired by vibrations of the harvesting machine and shocks when the harvesting machine travels over uneven ground.
DE 195 41 167 A describes a combine harvester in which the volume of the harvested crops in the grain elevator is detected optically. Furthermore, downstream of the grain elevator, a calibrating device is provided, in the form of a container which is equipped with a balance and into which, when quantity measurement is switched on, the harvested crops are diverted at specific time rates upon an operator's input or after a change in the type of harvested crops. The calibrating device serves for detecting the mass of a quantity of the harvested crops, the volume of which is likewise known, so that the optically detected volume of the harvested crops can subsequently be converted into a mass on the basis of the values of the calibrating device. There is still the disadvantage here, likewise, that the density of the harvested crops may change briefly, but, in unfavorable cases, this cannot be detected or can be detected only late by the calibrating device which becomes active only from time to time, so that there is still the risk of faulty measurement values for the mass.
DE 42 00 770 A describes a measurement apparatus for determining the fillability of tobacco material which is correlated with the density. The material is transported on a conveyor belt and the height of the material above the conveyor belt is detected by means of a laser sensing device, while the volume of the material is determined on the basis of the known conveying speed. At the same time, the conveyor belt is weighed, in order to determine the mass of the material. The density is then calculated by dividing the mass by the volume in order to obtain information on the fillability of the material. Since the throughput is essentially constant because the measurement apparatus is used in the cigarette production plant, the mass values which are susceptible to faults in the case of lower throughputs and which may arise due to the weighing of the conveyor belt together with the material do not present any problems with regard to the application described. On account of these faults, however, the measurement apparatus is not suitable for use in harvesting machines.
Finally, DE 198 08 148 A, considered as generic, describes an arrangement for determining the earth mass fraction in conveyed streams of agricultural products, such as sugar beet or potatoes. The harvested crops are transported on a chain conveyor. The volume of the harvested crops is detected by means of a laser scanner sensing their surface, while the mass of the harvested crops is determined by weighing the chain conveyor. The density of the harvested crops is calculated by dividing the mass by the volume, and, finally, the earth fraction in the harvested crop is determined on the basis of a stipulated known standard bulk density. Even here, the problem that mass determination is susceptible to faults in the case of lower throughputs is not solved.